FATTY SUBSTANCES (GENERAL METHODS) 391
(a) Volumetricatty. The product of the esterification is dissolved in
ether and washed repeatedly with water to eliminate the mineral acid and
then diluted with 50 c.c. of neutral alcohol and titrated with N/io-potassium
hydroxide in presence of phenolphthalein : i c.c. N/io-KOH = 0-0346
gram of resin.
(b) Gmvimetrically. The esterification product is dissolved in 50 c.c. of
petroleum ether (b.pt. below So0), shaken well, and the aqueous acid liquid
separated. The petroleum ether solution is washed •with water and shaken
with 50 c.c. of an aqueous solution containing 0-5 gram of caustic potash
and 5 c.c. of alcohol. The resin acids pass into the aqueous alkaline solu-
tion, whilst the fatty esters remain dissolved in the petroleum ether. The
alkaline aqueous liquid is, therefore, separated and acidified, the resin acids
thus obtained being removed by shaking the liquid with ether ; the solvent
is then evaporated and the residue dried at 100° and weighed.
This method gives only approximately exact results, which are more accurate
with the volumetric than with the gravimetric method. Modifications have
been suggested by Fahrion I and by Wolff and Scholtze,2 but it is most commonly
used in its original form. For more exact determinations, the method of Twitchell
and Gladding may be used under the conditions laid down by Holde and Mar-
cusson.3 Another method for the determination of resin, based on the solu-
bility of the alkali resinates in acetone, has been proposed by Leiste and Stiepel.4
21. Maumene Number
This represents the rise in temperature
produced when the fatty substance is mixed
with concentrated sulphuric acid under
definite conditions. Various methods of
measuring this increase, based on the original
one of Maumene, have been suggested.
Nowadays suitable forms of apparatus are
used (thermo-oleometers), such as that of Jean5
or that of Tortelli.
Tortelli's thermo-oleometer consists of a
small glass vacuum-jacketed vessel A (Fig.
57), and a thermometer-stirrer B provided
with two glass vanes near the bulb. 20 c.c.
of the oil are pipetted into A, stirred for a
minute by rotation of the stirrer and the tem-
perature read (t). By means of another pipette
5 c.c. of sulphuric acid (D exactly 1-8413) are
allowed to flow on to the oil while the stirrer is
rotated rapidly backwards and forwards and
kept just in contact with the bottom of the
vessel. The stirring is continued until the
1 Chem. Rev. Fett. Ind., 1911, p. 239.
8 Mitt. aus. dem Kgl. Matenalpv. Ami., 1902, p. 40.
4 Chem. Zentralbl., 1914, I, p. 577-
5 See F. Jean : CMmie analytique des mati&res grasses.
2 Chem. Zeit,, 1914, p. 369.j hour, when the saponification is complete. After an hour's rest,